In recent years, flat panel displays are used for various products and fields, and there is a need for flat panel displays further increased in size, improved in image quality, and having lower power consumption.
Under such circumstances, organic EL devices including organic electroluminescent elements (hereinafter referred to also as organic EL elements) that utilize electroluminescence of organic materials are attracting increasing attention as display units for all-solid state flat panel displays having excellent features such as capability of low voltage operation, fast responsiveness, and self-light emission.
An organic EL device includes, for example, a substrate such as a glass substrate, thin film transistors (TFTs) disposed on the substrate, and organic EL elements connected to the TFTs. Each of the organic EL elements has a structure in which a first electrode an organic electroluminescent layer (hereinafter referred to also as an organic EL layer), and a second electrode are stacked in this order. The first electrode is connected to a TFT. The organic EL layer has a structure in which layers such as a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer are stack.
An organic EL device for a full-color display generally includes organic EL elements of three colors, i.e., red (R), green (G), and blue (B), as sub-pixels. These sub-pixels are arranged in a matrix form to form pixels each composed of three color sub-pixels. These organic EL elements are caused to emit light from desired luminances in a selective manner to display an image.
For example, in a previously disclosed multi-color light-emitting element, a plurality of organic EL elements each having an organic compound layer including a light-emitting layer are disposed between a reflecting electrode and a transparent electrode. The plurality of organic EL elements include those with at least two different light-emission spectra, and light-emitting regions of the organic EL elements with different light-emission spectra are positioned at different positions in a thickness direction within the light-emitting layers according to the different light-emission spectra (see, for example, PTL 1).
PTL 1 discloses a method in which only a given region in each light-emitting layer is doped with a light-emitting guest material. This method is described in [0049] in PTL 1.
To produce the above-described organic EL device, light-emitting materials are formed into patterns of the light-emitting layers that correspond to the organic EL elements (sub-pixels) with different colors.
The following methods have been proposed to form the patterns of the light-emitting layers. In one method, a vapor deposition mask substantially equal in size to a substrate is brought into contact with the substrate, and then vapor deposition is performed (this method may be hereinafter referred to as a contact deposition method). In another method, a vapor deposition mask smaller in size than a substrate is used, and vapor deposition is performed over the entire substrate while the substrate is moved relative to the mask and an evaporation source (this method may be hereinafter referred to as a gap deposition method).